Fiber-optic technology has now advanced to the point where numerous commercial applications exist. For example, fiber optics are now replacing conventional underground telephone lines and are used for transmitting cable TV signals.
Fiber-optic cables may consist of a single filament or several filaments or even hundreds of optical fibers, but each fiber is a wholly independent optical waveguide in its operation, in that it contains and transmits the signals completely within each fiber and an almost zero field of optical energy is produced which may be externally detected or monitored in any way. Consequently, fiber optical signal information transmission provides a highly secure system. Thus they are being applied to computers for interconnecting mainframes to peripherals.
One of the most promising applications is the replacing of conventional metal wire in aircraft with fiber-optics. Not only are the fiber-optic cables lighter in weight, but the possibility of electro-magnetic interference is eliminated.
Unfortunately, generally available photometric test equipment is ill-suited to fiber-optic component and system evaluation. Radiometric measurements outside the visible spectrum are usually required and the mechanical means to couple the fibers' emitting signals and detection devices to standard instrumentation is frequently nonexistent or limited to providing comparative readings. Not only must the integrity of the fiber-optic filament be established but also the light source whether it be light-emitting diode or laser diode, and preferably while these components remain installed.
The prior art systems in general deal only with fault detection in fiber-optic cables and require removal of the cable from the system for checking of integrity. For example, U.S. Pat. No. 3,884,585, Fiber Break Detection Method for Cables Using Multi-Fiber Optical Bundles, by Robert L. Lebduska, discloses a method of detecting broken fibers or filaments in a fiber-optic bundle. The procedure requires that individual bundles be removed and placed in a test fixture in which one end of the bundle is illuminated with a light source and the transmitted light emitting from the face of the receiving cable end is magnified by a microscope. A second light is used to illuminate the surface of the receiving cable end in order to enable the faces of the broken fibers to be distinguishable from the remaining background.
Another example is U.S. Pat. No. 4,070,118, Method and an Arrangement for Fault Location in a Glass Fiber Optical Waveguide, by Stefan Maslowski et al., which discloses a method of locating faults in a glass fiber by using a laser device to feed light pulses into the fiber, feeding the light pulses reflected back from the fault in the fiber into the laser device allowing the determination of the physical location of the fault from the known propagation time of the reflective pulses. While this device can locate faults without requiring the removal of the fiber-optic cable, it cannot be used to test emitters or to monitor transmitted signals.
Available apparatus for determining the characteristics of emitters typically have the disadvantage of requiring their removal from the system for check out. For example, U.S. Pat. No. 3,752,980, Apparatus for Measuring Electroluminescent Device Parameters, by Richard Wayne Dixon et al., discloses a method to determine the output characteristics of an electroluminescent device which is accomplished by installing the device in a test circuit wherein the output characteristics are measured as a function of the amplitude of an input current pulse. Another disadvantage of such an apparatus is that it cannot be used to check out fiber-optic cables nor can it determine if specific light signals are being transmitted.
It is also very important to be able to determine if both transitory and repetitive signals are being transmitted from one station to another, for example, from a main computer to peripherals. The transitory signals may be of short duration and being invisible radiant energy, not electrical wave forms, they simply cannot be readily observed by the technician on an oscilloscope or the like. It is also desirable to have means to record the received signals for subsequent detailed analysis. Another desirable capability is to be able to convert received light signals to audio signals to provide additional monitoring capability.
Thus, it is a primary object of this invention to provide a method of detecting both transitory and repetitive light signals in optical communication systems without requiring removal of system components.
A further object of this invention is to provide means of converting received light signals to radiometric or photometric signals.
Another object of this invention is to provide a means to convert received light signals to audio signals.
Still another object of this invention is to provide a video output of received repetitive and transitory light signal.